1. Field of the Invention
The present invention relates generally to a mobile communication terminal, and in particular, to a quick paging method for decreasing unnecessary battery consumption by a mobile terminal in a shadow area or a hand off region.
2. Description of the Related Art
A 1×MS (Multiple Carrier) CDMA (Code Division Multiple Access) mobile communications system, which complies with the 3G (third generation) mobile communications standard proposed by the ITU (International Telecommunication Union), not only supports high-speed packet data transmission of 153.6 Kbps or more, but also provides various applications and a long call time while occupying a relatively small space compared with the existing systems. In addition, the 1×MS CDMA mobile communications system provides various functions such as high-speed forward power control and a new modulation/coding scheme.
In particular, a mobile terminal based on the 3G mobile communications standard improves a call standby time using a quick paging channel (QPCH). In the 2G (second generation) mobile communication a terminal is assigned a given time slot out of successive time slots each having the same time period (e.g., 80 ms) in a paging channel. The time slot of the paging channel carries various control messages transmitted from a base station to a mobile terminal, such as a paging message. In a paging method, so as to read a message of a time slot assigned to a mobile terminal itself, the mobile terminal must wake up one time slot ahead of the assigned time slot. However, compared to the paging method, a quick paging method considerably reduces this time and prevents the mobile terminal from waking up unnecessarily using a paging indicator bit, thereby remarkably reducing consumption of power by the mobile terminal in an idle mode.
FIG. 1 illustrates an operational principle of a quick paging channel utilizing two indicator bits. Referring to FIG. 1, when there is no request from a user or a system, a mobile terminal maintains a sleep state 13 in an idle mode so as to prevent unnecessary power consumption. In the sleep state 13, no power is supplied to communication-related circuits of the mobile terminal. A base station repeatedly transmits a first indicator bit 11 and a second indicator bit 12 at given intervals over the quick paging channel, and the mobile terminal receives and demodulates the first indicator bit 11 and the second indicator bit 12 to determine their values. When it is determined that the values of both the first and second indicator bits are ‘1’ or erased, the mobile terminal wakes up to read a time slot assigned thereto (Wake-up state 14) and demodulates the assigned time slot of a paging channel.
Here, strength of a pilot channel signal received by the mobile terminal is used as a criterion for judging whether the indicator bits are erased or not. This is because the strength of the pilot channel signal transmitted by the base station serves as a criterion for determining transmission signal strength of other channels. Equation (1) below is an example of a criterion equation for judging whether the indicator bits are erased.pilot_Ec/Io<−10 dB  (1)
In Equation (1), ‘pilot_Ec’ indicates chip energy of a pilot channel, and ‘ITO’ represents the total reception power.
Meanwhile, in a downtown area where there are many buildings, subways and complicated roads, the mobile terminal can often enter a shadow area where an electric wave cannot be received or is received very weakly. In another case, the mobile terminal can enter a hand off region, a boundary area between cells. In these cases, a state satisfying Equation (1) (i.e., an erasure of the indicator bit) occurs frequently unless the mobile terminal is removed from the shadow area or the hand off region. Whenever the state satisfying Equation (1) happens, the mobile terminal enters a wake-up mode and modulates the paging channel. However, the conventional art does not provide a method for avoiding the frequent wake-up phenomenon in the shadow area or the hand off region, and thus cannot prevent a decrease in efficiency of the quick paging method.